When maneuvering watercraft during docking or in other space-restricted areas, it is often desirable to be able to propel the hull of the watereraft laterally. Side thrusters have been developed that discharge directed streams of water from ports in a boat hull below the waterline, typically in the bow of the vessel. The thrust of the discharge stream creates a reaction force that propels the bow of the vessel in the opposite direction of the stream discharge.
Conventional side thrusters typically include a pump mounted within the hull of the vessel that draws water from outside the hull, and that discharges a pressurized fluid stream from a nozzle or other through-hull port. One such conventional side-thruster is disclosed by U.S. Pat. No. 3,593,686 to Cooper, which utilizes an electric motor-driven squirrel-cage type impeller to generate the thrust steam. The impeller pump draws water from a radially oriented inlet and discharges the water from a radially oriented outlet. Somewhat similar radially-fed impeller pump thrusters are disclosed by U.S. Pat. Nos. 5,289,793 to Akeer and 4,807,552 to Fowler.
Other conventional side thrusters include a propeller mounted within a conduit that produces a fluid stream for development of thrust. These include: U.S. Pat. Nos. 3,903,833 to Lais et at.; 5,140,926 to Denston; 4,470,364 to Kitaura et at.; and 5,072,579 to Gongwer.
Such conventional side thrusters have varying degrees of efficiency, which affects both the power required to operate the thruster and the level of thrust force produced.
Many such conventional side thrusters include outlets on each side of the vessel, for selective discharge of a thrust stream or streams from the port or starboard sides. Most such conventional side thrusters include a series of valves that are opened and closed to direct the thrust stream to one or the other side of the vessel.